Filler for grinding wheels



United States Patent 3,113,006 FILLER FiJR GRINDING WHEELS Harry S. Kibbey, Morrow, Ohio, assignor to The Cincinnati Milling Machine (10., Cincinnati, Ohio, a corporation of Ohio No Drawing. Filed Jan. 30, 1%1, Ser. No. 85,492 4 Claims. (Cl. 51-298) This invention relates to the manufacture of abrasive articles such as grinding wheels and more particularly to grinding wheels incorporating novel and improved fillers.

One widely used type of grinding wheel is essentially composed of abrasive grains bonded in a matrix comprising a synthetic resin, commonly a phenolic resin, having an inorganic filler in powder form dispersed therethrough. It is known that fillers of this type give stability to the molded product during cure and are also a necessary component of a high-strength bond, particularly in the case of hard, dense grinding wheels.

It has been generally accepted that fillers possessing special properties are required on severe dry grinding operations, especially when the grinding of highly corrosion resistant metals is involved. Billet snagging and cutting off operations typify cases in which special fillers are required.

While several possible mechanisms have been suggested to account for the improved performance obtained when fillers are incorporated in the bond, it is not possible to demonstrate conclusively which if any of these proposed mechanisms is in fact responsible for the improved results obtained. In general the utility of particular fillers or classes of fillers must be established by experiment. This is especially true of blends of different fillers, which in some cases have been found to exhibit a synergistic effect. Accordingly empirical criteria have been found to be essential in evaluating such fillers.

In the present specification, two empirical criteria will be used for indicating the relative effectiveness of the various filler materials referred to, namely, grinding ratio and metal removal rate. Grinding ratio is expressed as the number of cubic inches of metal removed for each cubic inch of wheel wear. For example, if in the course of a grinding operation, 25 cubic inches of metal is removed from the piece of metal being ground and at the same time 5 cubic inches of the grinding wheel is worn away, the grinding ratio will be 5 .0. Metal removal rate is expressed in cubic inches per minute. If for example 25 cubic inches of metal is removed from the piece of metal being ground over a period of five minutes, the metal removal rate is 5.0. It is evident that grinding ratio and metal removal rate as thus defined Will vary as a function of both grinding wheel properties and the nature of the metal being ground. Hence valid comparisons can be achieved only by grinding a particular metal stock under standardized conditions.

It is an object of the present invention to provide a resin-bonded abrasive article having improved grinding properties. It is another object of the invention to provide a resin-bonded abrasive grinding wheel containing a novel filler that confers improved grinding properties on the wheel, especially when the wheel is used for severe dry grinding operations such as billet snagging and cutoff operations. It is still another object of the invention to provide a resin-bonded abrasive grinding wheel which exhibits an improved grinding ratio and/or metal removal rate. It is a still further object of the invention to provide a grinding wheel that is free from the phenomenon known as loading i.e., a wheel that does not accumulate particles of ground metal at the grinding surface thereof. Other objects of the invention will be in part obvious and in part pointed out hereafter.

The present invention is predicated upon the discovery "ice that resinoid grinding wheels having the improved properties indicated above can be made by employing as a filler a complex fluoride from the class having the general formula AnMF +4 wherein A is an alkali metal, M is an element of group IV of the periodic table selected from the group consisting of silicon, zirconium and titanium, F is fluorine and n is 1 or 2. The compounds thus defined can be used alone as a filler, or they can be blended in various proportions with other known fillers as more fully described hereafter. Grinding wheels incorporating some of the fillers as defined above exhibit both improved grinding ratios and improved metal removal rates in relation to wheels made with prior fillers, whereas wheels incorporating other fillers of the .type defined show improvement in respect to one or the other of these properties. However all of the fillers defined above when properly incorporated in grinding wheels as taught herein appear to give either an improved grinding ratio or an improved metal removal rate or both.

It has been found that small percentage additions of the present fillers to formulations containing prior art fillers produce significant improvements in grinding ratio and/ or metal removal rate over similar formulations containing the prior art fillers alone. Addition of the present fillers in small percentages permits relatively inexpensive prior filers that impart high strength to resin-bonded snagging formulations to be used as a high percentage of the total filler and still maintain attractive performance levels.

As indicated above, the present fillers may, in general, be used as the sole filler and when so used have been found to be operative over a relatively wide range, e.g., 5% to 40% of the volume of the bond. They may also be blended with other known fillers such as cryolite, iron sulfide (pyrites), Zinc sulfide and the like. In such blends the present fillers are desirably used to the extent of at least about 10% of the total volume of filler. On the other hand, since most of the present fillers can be used as the sole filler in the formulations, the upper limit on the amount used in a blend is that is, the useful range is 10% to 100%.

In order to point out more fully the nature of the present invention the following examples are given of illustrative embodiments of grinding wheels incorporating the invention.

EXAMPLE 1 A number of snagging wheels were made up as described herein incorporating various fillers as specified in Table 1 below. For purposes of comparison, the data of Table 1 include values for a number of conventional fillers, e.g., cryolite (N'a A1F pyrite (FeS and inc sulfide. These snagging wheels were tested in accordance with the method described herein to determine grinding ratio and metal removal rate and the values are set forth in Table 1. The formulation employed in making these grinding wheels was as follows:

58.63 parts by volume of A1 0 abrasive grain /3 each,

12 grit, 14 grit, l6 grit) 8.67 parts by volume of liquid resin (50% Varcum 8121,

50% furfural) 1.53 parts by volume calcium oxide 17.96 parts by volume of powdered phenolic resin (Varcum 3034) 13.22 parts by volume of filler The abrasive grain was mixed with the liquid resin in a mixer to cause the liquid resin to coat the abrasive. The powdered phenolic resin, calcium oxide and filler were separately blended in a mixer and the wetted abrasive was then added to and mixed with the blended powders to uniformly coat each particle of abrasive with the blended powdered materials.

The resulting mixture was cold-molded into a wheel A thick at a pressure of about 2 tons per square inch to give the wheel a grain density of 36.41 grams per cubic inch. Wheel density varied with specific gravity of the filler material and ranged from 48.0 grams per cubic inch to 53.0 grams per cubic inch. The molded wheel was cured in a convection oven to a top temperature of 365 F.

Grinding tests to evaluate these wheels were conducted on a cut-off machine, cutting off one inch square bar stock of 430 stainless steel. The machine was operated at a constant pressure of 690 pounds per inch of wheel width and wheel speed was 9500 surface feet per minute. The time required per cut and the wheel wear in inches on the diameter of the Wheel were measured. Since a known volume of metal was removed in each cut, the metal removal rate in terms of cubic inches per minute and the grinding ratio in volume of metal removed per volume of wheel wear could be determined from these data. The results are given in Table 1 below.

In Table 1, the values are based upon cryolite as a standard filler. That is to say, the cryolite filler is assumed to have a unit grinding ratio and a unit metal removal rate. Thus the values given are relative rather than absolute. In the case of the blends the percentages given are by volume.

Table 1 Grinding Metal Filler Ratio Removal Rate Cryolite 1.00 1. Pyrite .98 91 Z118..." .97 .93 KgSiFa .91 1.15 90% Pyrite-% I 2siF6 1. 41 1. 04 80% Pyrite% :K2SiFc. 1. 46 1.12 50% Pyrite50% KzsiFu 1. 39 1.18 90% Pyrite10% NazSiF 1.65 1.08 50% ZnS-50% KzSiF 1. 09 1.19

The foregoing data clearly brmg out the synergrstic effect that is obtained by blend-ing the alkali metal silico fluorides with pyrite and zinc sulfide.

EXAMPLE 2 A series of grinding wheels was made up in accordance with the procedure of Example 1 but using as fillers the several alkali metal zirconium fluorides and blends thereof indicated in Table 2 below, rather than the alkali metal silicofluoride fillers of Example 1. In the wheels of this example, the filler comprised 42.4% by volume of the bond. The wheels were tested by grinding 430 stainless steel as in Example 1 and the results are given in Table 2. As in Example 1, the blends are expressed in percent by volume.

4 The data of Table 2 further illustrate both the superiority of the present fillers per se and the synergistic effect obtainable by blending these fillers with previously known fillers.

EXAMPLE 3 Wheels were made up in accordance with the general procedure of Example 1 but utilizing potassium titanium fluoride (K TiF and a blend of potassium titanium fluoride with pyrite as the fillers thereof. In these wheels the filler comprised 42.4% by volume of the bond. These wheels when tested on 430 stainless steel gave the results indicated in Table 3 below.

Table 3 Grinding Metal Filler Ratio Removal Rate Cryolitc l. 00 1. 00 :KzTlFB 1.18 1.28 Pyrite(S0), KzTiFqQO) 1.06 1. 06

EXAMPLE 4 Wheels were made up in accordance with the general procedure of Example 1 but using the fillers indicated in Table 4 below. In these Wheels the filler comprised 42.4% by volume of the bond, except in the wheel wherein sodium zirconium fluoride was used alone, in which case the filler was 30.8% by volume of the bond. These wheels were tested by grinding C 1018 steel instead of the 430 stainless steel of the preceding examples. The test results are given in Table 4.

The data of Table 4 show that in the grinding of C 1018 steel the wear resistance of wheels incorporating the present fillers is strikingly greater than that of wheels employing cryolite as a filler.

From the foregoing description it is apparent that the present invention provides an economic means of improving the performance of grinding wheels incorporating a relatively large proportion of inexpensive filler. The improvement achieved by utilizing relatively small amounts of the novel fillers of the present invention in a blended filler is under suitable conditions considerably more than proportional to its concentration in the blend. In some cases the performance obtained with the blended fillers is superior to that obtained with either filler alone. Moreover it has been found that when the present fillers are used there is much less tendency for the surface of the Wheel to become loaded with metal particles. This low loading property is especially important in the working of aluminum and its alloys which are particularly difficult to grind because of the wheel loading problem.

It is of course to be understood that the foregoing examples are intended to be illustrative only and that numerous changes can be made in the ingredients and proportions described therein without departing from the spirit of the invention :as defined in the appended claims.

I claim:

1. In an abrasive article essentially composed of abrasive grains bonded with a synthetic resin bond having a filler dispersed therethrongh, the improvement which comprises incorporating in said filler from 10% to by volume of potassium silicofluoride.

2. In an abrasive article essentially composed of abrasive grains bonded with a synthetic resin bond having a filler dispersed therethrough, the improvement which comprises incorporating in said filler from 10 to 100% by volume of sodium silicofluoride.

3. In an abrasive article essentially composed of abrasive grains bonded with a synthetic resin bond having a filler dispersed therethrough, the improvement which comprises incorporating in said filler from 10% to 100% by volume of sodium zirconium pent-afluoride.

4. In an abrasive article essentially composed of abra- References Cited in the file of this patent UNITED STATES PATENTS 2,216,135 Rainier Oct. 1, 1940 2,939,777 Gregor et a1 June 7, 1960 2,940,841 Gregor et a1 June 14, 196 0 

1. IN AN ABRASIVE ARTICLE ESSENTIALLY COMPOSED OF ABRASIVE GRAINS BONDED WITH A SYNTHETIC RESIN BOND HAVING A FILLER DISPERSED THERETHROUGH, THE IMPROVEMENT WHICH COMPRISES INCORPORATING IN SAID FILLER FROM 10% TO 100% BY VOLUME OF POTASSIUM SILICOFLUORIDE.
 4. IN AN ABRASIVE ARTICLE ESSENTIALLY COMPOSED OF ABRASIVE GRAINS BONDED WITH A SYNTHETIC RESIN BOND HAVING A FILLER DISPERSED THERETHROUGH, THE IMPROVEMENT WHICH COMPRISES INCORPORATING IN SAID FILLER FROM 10% 100% BY VOLUME OF POTASSIUM TITANIUM FLUORIDE. 